http://www.timesonline.co.uk/tol/news/environment/article7086746.ece

IF you thought it was cold in Britain for the time of year, you should see what is happening around the North Pole. Scientists have discovered that the size of the Arctic ice cap has increased sharply to levels not seen since 2001.

A shift in the chilly winds across the Bering Sea over the past few months has caused thousands of square miles of ocean to freeze.

The same phenomenon, known as the Arctic Oscillation, is also partly responsible for the cold winter experienced in northern Europe and eastern America.

It allowed icy blasts of air to escape from the Arctic and make their way southwards. Provisional Met Office figures for December to February suggest the UK had its coldest winter since 1979, with an average temperature of 1.6C — a full 2.1C below normal. Last week a teenager was killed in Scotland when a school bus crashed in the snow — just days into British Summer Time.

The Arctic Oscillation usually acts like a ring of strong winds circulating anti-clockwise around the North Pole to dam up cold Arctic air. This year it has turned “negative”, meaning the ring has broken down, allowing blasts of cold air to escape to lower latitudes.

Mark Serreze, director of the National Snow and Ice Data Center (NSIDC) in Colorado, is surprised by the Arctic’s recovery from the great melt of 2007 when summer ice shrank to its smallest recorded extent.

“It has been a crazy winter with Arctic ice cover growing and very cold weather in northern Europe and eastern America all linked to this strongly negative Arctic Oscillation,” Serreze said.

Vicky Pope, a Met Office scientist, said the Arctic Oscillation had affected weather across the hemisphere. “It also played a part in the very warm weather experienced in the Mediterranean, and western Canada, where the winter Olympics were at risk of too little snow,” she said.

Scientists emphasise that the regrowth of ice in the Arctic and the fierce US blizzards are natural variations in weather which have little relevance for long-term climate change.

“Records kept by Nasa show that in January and February global average temperatures were actually well above the long-term average by around 0.7C,” Serreze said.

Such caution contrasts with the warnings issued by scientists in 2007 when the north polar ice cap suffered a spectacular summer melt.

It hit an all-time low size of 1.65m square miles, about 39% below average, prompting many scientists, including some at the NSIDC, to suggest that global warming had pushed the Arctic to a tipping point from which it might not recover.

By last summer, however, the ice cap had expanded to 2m square miles and this year’s figures show it approaching normal levels for the time of year.

“In retrospect, the reactions to the 2007 melt were overstated. The lesson is that we must be more careful in not reading too much into one event,” Serreze said.

The Met Office had taken a more cautious approach in 2007, warning that the melting was a natural variation so the ice was likely to recover.

Scientists have made mistakes over other short-term trends such as increases in tropical storms. In 2004-5 an increase in the number and severity of storms, including Hurricane Katrina, prompted some researchers to suggest a link with global warming — but this was then followed by a decline in storms.

Similar fears were raised in 2005 when scientists at Southampton University published research showing that some deep Atlantic Ocean currents, linked to the Gulf Stream, had slowed by a third.

They issued a press release entitled “Could the Atlantic current switch off?” which suggested that circulation in the ocean, which gives Europe its temperate climate, might shut down. But more recent studies have shown that such currents slow down and speed up naturally, so short-term changes cannot be seen as evidence of global warming.